This invention relates to a communications network for collecting data from remote data generating stations, and more particularly a radio based system for sending data from a plurality of network service modules, with each network service module attached to a meter, and communicating through remote cell nodes and through intermediate data terminals, to a central data terminal.
Many attempts have been made in recent years to develop an automatic meter reading system for utility meters such as used for electricity, gas and water, which avoids meter reading personnel inspecting and physically noting the meter readings. There are, of course, many reasons for attempting to develop a system of this type.
Most of the prior art systems have achieved little success. The system, which has achieved some success or is most widely used has an automatic meter reading unit mounted on an existing meter at the usage site and includes a relatively small transmitter and receiver unit of very short range. The unit is polled on a regular basis by a traveling reading unit, which is carried around the various locations on a suitable vehicle. The traveling reading unit polls each automatic meter reading unit in turn to obtain stored data. This approach is of limited value in that it requires transporting the equipment around the various locations and, hence, only very infrequent, for example monthly, readings can be made. The approach avoids a meter reader person actually entering the premises to physically inspect the meter which is of itself of some value but only limited value.
Alternative proposals in which reading from a central location is carried out have been made but have achieved little success. One proposal involves an arrangement in which communication is carried out using the power transmission line of the electric utility. Communication is, therefore, carried out along the line and polls each remote reading unit in return. This device has encountered significant technical difficulties.
Another alternative attempted to use the pre-existing telephone lines for communication. The telephone line proposal has a significant disadvantage since it must involve a number of other parties, in particular the telephone company, for implementing the system. The utility companies are reluctant to use a system which cannot be entirely controlled and managed by them.
A yet further system using radio communication has been developed by Data Beam, which was a subsidiary of Connecticut Natural Gas. This arrangement was developed approximately in 1986 and has subsequently received little attention and it is believed that no installations are presently operative. The system includes a meter reading device mounted on the meter with a transmitting antenna which is separate from the meter reading device. The transmitting antenna is located on the building or other part of the installation site which enables the antenna to transmit over a relatively large distance. The system uses a number of receiving units with each arranged to receive data from a large number of transmitters, in the range of 10,000 to 30,000. The transmitters, in order to achieve maximum range, are positioned to some extent directionally or at least on a suitable position of the building to transmit to the intended receiving station. This arrangement leads to using a minimum number of receiving stations for optimum cost efficiency.
The separate transmitter antenna, however, generated significant installation problems due to wiring the antenna through the building to the transmitter and receiver. The anticipated high level of power used for transmitting involved very expensive battery systems or very expensive wiring. The proposal to reduce the excessive cost was to share the transmission unit with several utilities serving the building so that the cost of the transmitter could be spread, for example, between three utilities supplied to the building. Such installation requires separate utility companies to cooperate in the installation. While this might be highly desirable, such cooperation is difficult to achieve on a practical basis.
In order to avoid timing problems, the meter reading units were arranged to communicate on a random time basis. However, the very large number, up to 30,000, of meter reading units reporting to a single receiving station, leads to a very high number of possible collisions between the randomly transmitted signals. The system, therefore, as proposed, with daily or more often reporting signals could lose as many as 20% to 50% of the signals transmitted due to collisions or interference which leads to a very low efficiency data communication. The use of transmitters at the meter reading units which are of maximum power requires a larger interference protection radius between systems using the same allocated frequency.
An alternative radio transmission network is known as ALOHA. ALOHA has a number of broadcasting stations communicating with a single receiving station, with the broadcasting stations transmitting at random intervals. In the ALOHA system, collisions occur so that messages are lost. The solution to this problem is to monitor the retransmission of the information from the receiving station so that each broadcasting station is aware when its transmission has been lost. Each broadcasting station is then programmed to retransmit the lost information after a predetermined generally pseudorandom period of time. The ALOHA system requires retransmission of the information from the receiving station to take place substantially immediately and requires each broadcasting station to also have a receiving capability.
Cellular telephone networks are implemented on a wide scale. Cellular systems, however, use and allocate different frequencies to different remote stations. While this is acceptable in a high margin use for voice communications, the costs and complications cannot be accepted in the relatively lower margin use for remote station monitoring. The technology of cellular telephones leads to the perception in the art that devices of this type must use different frequency networks.
While theoretically automatic meter reading is highly desirable, it is, of course, highly price sensitive and hence it is most important for any system to be adopted for the price per unit of particularly the large number of meter reading units to be kept to a minimum. The high cost of high power transmission devices, receiving devices, and battery systems generally leads to a per unit cost which is unacceptably high.
A general object of the invention is a communications network for communicating data from a plurality of network service modules to a central data terminal.
Another object of the invention is a communications network which is suitable for an automatic meter reading system.
A further object of the invention is a communications network for collecting data from remote data generating stations that is simple and economic to install and maintain.
A still further object of the invention is a communications network for collecting data from network service modules that is spectrum efficient, and has inherent communication redundancy to enhance reliability and reduce operating costs.
An additional object of the invention is an open architecture communication network which accommodates new technology, and allows the network operator to serve an arbitrarily large contiguous or non-contiguous geographic area.
According to the present invention, as embodied and broadly described herein, a wide area communications network is provided for sending data from a plurality of network service modules to a central data terminal. The wide area communications network collects NSM data generated by a plurality of physical devices located within a geographical area. The physical devices may be, for example, a utility meter as used for electricity, gas or water. The wide area communications network comprises a plurality of network service modules, a plurality of remote cell nodes, a plurality of intermediate data terminals, and a central data terminal. Each network service module is coupled to a respective physical device.
The network service module (NSM) includes NSM-receiver means, NSM-transmitter means, and NSM-processor means, NSM-memory means and an antenna. The NSM-receiver means, which is optional, receives a command signal at a first carrier frequency or a second carrier frequency. In a preferred mode of operation, the NSM-receiver means receives the command signal on the first carrier frequency for spectrum efficiency. The wide area communications network can operate using only a single carrier frequency, i.e., the first carrier frequency. The command signal allows the oscillator of the NSM-transmitting means to lock onto the frequency of the remote cell node, correcting for drift. Signaling data also may be sent from the remote cell node to the network service module using the command signal.
The NSM-processor means arranges data from the physical device into packets of data, transfers the data to the NSM-memory means, and uses the received command signal for adjusting the first carrier frequency of the NSM transmitter. The NSM data may include meter readings, time of use and other information or status from a plurality of sensors. The NSM-processor means, for all network service modules throughout a geographical area, can be programmed to read all the corresponding utility meters or other devices being serviced by the network service modules. The NSM-processor means also can be programmed to read peak consumption at predetermined intervals, such as every 15 minutes, throughout a time period, such as a day. The NSM-memory means stores NSM data from the physical device. The NSM-processor means can be programmed to track and store maximum and minimum sensor readings or levels throughout the time period, such as a day.
The NSM-transmitter means transmits at the first carrier frequency the respective NSM data from the physical device as an NSM-packet signal. The NSM-packet signal is transmitted at a time which is randomly or pseudorandomly selected within a predetermined time period, i.e., using a one-way-random-access protocol, by the NSM-processor means. The NSM-transmitter includes a synthesizer or equivalent circuitry for controlling its transmitter carrier frequency. The NSM-transmitter means is connected to the antenna for transmitting multi-directionally the NSM-packet signals.
A plurality of remote cell nodes are located within the geographical area and are spaced approximately uniformly, such that each network service module is within a range of several remote cell nodes, and so that each remote cell node can receive NSM-packet signals from a plurality of network service modules. The remote cell nodes preferably are spaced such that each of the network service modules can be received by at least two remote cell nodes. Each remote cell node (RCN) includes RCN-transmitter means, RCN-receiver means, RCN-memory means, RCN-processor means, and an antenna. The RCN-transmitter means transmits at the first carrier frequency or the second carrier frequency, the command signal with signaling data. Transmitting a command signal from the RCN-transmitter means is optional, and is used only if the NSM-receiver means is used at the network service module as previously discussed.
The RCN-receiver means receives at the first carrier frequency a multiplicity of NSM-packet signals transmitted from a multiplicity of network service modules. Each of the NSM-packet signals typically are received at different points in time, since they were transmitted at a time which was randomly or pseudorandomly selected within the predetermined time period. The multiplicity of network service modules typically is a subset of the plurality of network service modules. The RCN-receiver means also receives polling signals from the intermediate data terminal, and listens or eavesdrops on neighboring remote cell nodes when they are polled by the intermediate data terminal.
The RCN-memory means stores the received multiplicity of NSM-packet signals. The RCN-processor means collates the NSM-packet signals received from the network service modules, identifies duplicates of NSM-packet signals, and deletes the duplicate NSM-packet signals. When a polling signal is sent from an intermediate data terminal (IDT), the RCN-transmitter means transmits at the first carrier frequency the stored multiplicity of NSM-packet signals as an RCN-packet signal.
When a first remote cell node is polled with a first polling signal by the intermediate data terminal, neighboring remote cell nodes receive the RCN-packet signal transmitted by the first remote cell node. Upon receiving an acknowledgment signal from the intermediate data terminal, at the neighboring remote cell nodes, the respective RCN-processor means deletes from the respective RCN-memory means messages, i.e., NSM-packet signals, received from the network service modules that have the same message identification number as messages transmitted in the RCN-packet signal from the first remote cell node to the intermediate data terminal.
The plurality of intermediate data terminals are located within the geographic area and are spaced to form a grid overlaying the geographic area. Each intermediate data terminal includes IDT-transmitter means, IDT-memory means, IDT-processor means and IDT-receiver means. The IDT-transmitter means includes a synthesizer or equivalent circuitry for controlling the carrier frequency, and allowing the IDT-transmitter means to change carrier frequency. The IDT-transmitter means transmits preferably at the first carrier frequency, or the second carrier frequency, the first polling signal using a first polling-access protocol to the plurality of remote cell nodes. When the first polling signal is received by a remote cell node, that remote cell node responds by sending the RCN-packet signal to the intermediate data terminal which sent the polling signal. If the intermediate data terminal successfully receives the RCN-packet-signal, then the IDT-transmitter means sends an acknowledgment signal to the remote cell node.
The IDT-receiver means receives the RCN-packet signal transmitted at the first carrier frequency from the remote cell node which was polled. Thus, after polling a plurality of remote cell nodes, the IDT-receiver means has received a plurality of RCN-packet signals.
The IDT-memory means stores the received RCN-packet signals. The IDT-processor means collates the NSM-packet signals embedded in the RCN-packet signals received from the plurality of remote cell nodes, identifies duplicates of NSM-packet signals and deletes the duplicate NSM-packet signals, i.e., messages from network service modules that have the same message identification number. In response to a second polling signal from a central data terminal, the IDT-transmitter means transmits a plurality of RCN-packet signals as an IDT-packet signal to the central data terminal.
The central data terminal (CDT) includes CDT-transmitter means, CDT-receiver means, CDT-processor means and CDT-memory means. The CDT-transmitter means transmits sequentially the second polling signal using a second polling access protocol to each of the intermediate data terminals. The CDT-receiver means receives a plurality of IDT-packet signals. The central data terminal, intermediate data terminals and the remote cell nodes may be coupled through radio channels, telephone channels, fiber optic channels, cable channels, or other communications medium. The CDT-processor means decodes the plurality of IDT-packet signals as a plurality of NSM data. The CDT-processor means also identifies duplicates of NSM data and deletes the duplicate NSM data. The CDT-memory means stores the NSM data in a data base.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.